ci: Fix testing feature combinations.

- First, the autocrypt feature has been removed in
    86f599542c.

  - Second, cargo now considers it an error to give an empty string to
    --features.

.gitlab-ci.yml

@@ -76,11 +76,9 @@ sq-features:
     matrix:
       - FEATURES:
         - ""
-        - "autocrypt"
-        - "autocrypt,compression-bzip2"
-        - "compression-bzip2"
+        - ",compression-bzip2"
   script:
-    - cargo test --no-default-features --features crypto-nettle --features $FEATURES
+    - cargo test --no-default-features --features crypto-nettle$FEATURES
   variables:
     CARGO_TARGET_DIR: /target
     CARGO_HOME: /cargo